Automatic re-set thermostatic circuit breaker



J. W. WELSH Nov. 12, 1963 AUTOMATIC RE-SET THERMOSTATIC CIRCUIT BREAKER Filed Nov. 1'7, 1959 -FIG.4

INVENTOR. James W. Weish BY MMMfi,

ATTORNEYS United States Patent goriporation, Brooklyn, N.Y., a corporation of New Filed Nov. 17, 1959, Ser. No. 853,487 1 Claim. (Q1. Mill-115.5)

This invention relates to automatic circuit breakers of the type having a threaded shell around a bodyand which may be screwed into a suitable receptacle in a fuse box, circuit breaker housing, or the like. More particularly, the invention relates to an automatic re-set type circuit breaker which can be substituted for the usual plug fuse.

A well-known type of circuit breaker, commonly used in household and automobiles, is the plug type of fuse. A plug fuse comprises a hollow body of dielectric material having an outer threaded shell of conductive metal and a central contact at its inner end. The shell and the central contact are interconnected by a relatively thin strip of fusible metal. This plug fuse may be threaded into a suitable receptacle where it is in series with a load circuit connected to the receptacle. Upon the load circuit drawing a current in excess of the rating of the plug type fuse, the fusible strip of metal melts and breaks to open the circuit.

When a plug type fuse thus breaks a circuit, it is no longer useful and must be taken out of its socket and discarded, being replaced by a new fuse. For this reason, a more modern practice is to replace the usual household fuse box by a circuit breaker housing containing, in place of the usual plug fuses, small circuit breakers which may be manually reset after they have opened a load circuit. However, circuit breakers of this type are relatively expensive and this has somewhat limited their market in competition with the usual plug fuse. Also, such circuit breakers must be manually re-set after they have opened a circuit and will not automatically close upon clearance of the fault in the circuit.

In accordance with the present invention, an automatically re-set circuit breaker is provided which has a housing substantially identical with that of the usual plug type fuse and therefore may easily be substituted for such a fuse and is as simply and inexpensively constructed. This automatic re-set circuit breaker utilizes a novel thermostatic element for interrupting the circuit whenever an overload occurs and for periodically reolosing the circuit to test the operative condition thereof, the thermostatic element remaining in the closed condition when the fault has been cleared from the circuit.

More specifically, in accordance with the present invention, I mount within the housing of the usual plug type fuse a monometal snap action vane type or circuit closer such as shown in FIG. 4 of my U.S. Patent No. 2,870,291 issued January 20, 1959. As described in said patent, this vane is circular in shape and has a slot extending .parallel to its circumference and throughout approximately 180 degrees, this slot dividing the vane into a main body section and a relatively narrower arcuate strip. The vane body portion is also formed with relatively elongated ridges or other deformations which are spaced from and diverge outwardly from the slot. When a current is passed through a vane of this type, the body portion and strip are differentially heated due to the great difference in their cross sectional area and, as a result, the strip portion expands relative to the body portion. This causes the body portion to snap from an initial deformed position, to which it is constrained by a foreshortening of the strip, to another position.

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Hence, if the vane is rigidly mounted adjacent substantially the center of its strip portion, the body portion will move relative to the strip portion. Thus, if a contact is secured to the body portion and engages with a relatively fixed contact, these two contacts will be separated upon snapping of the body portion relative to the strip portion. Preferably, the other terminal of the circuit through the vane extends from the center of the strip portion so that the current fiow through the strip portion is divided into two paths.

As an alternative, the strip portion may be heated by a high resistance wire wound therearound and insulated therefrom, and this wire may be connected at one end to the strip portion and at the other end to the terminal where the current enters or leaves the vane.

Circular snap action vanes of this type can be readily cut to fit within the dielectric housing of the usual plug fuse, and can be mounted therein in such a manner that the strip is supported from the dielectric housing and connected, either directly or by means of a high resistance winding wound therearound, to the threaded metal shell on the outer surface of the housing. The center contact usually found in such plug fuses is carried up to a fixed contact which is engaged by a contact on the body portion of the vane when the circuit is closed. Under normal current flow through a vane of this type, provided the parameters are properly selected, there will be no deflection of the body portion of the vane and the load circuit will remain completed. However, upon flow of current in excess of the pre-set rating, the heating of the strip will cause the body of the vane to snap upwardly or outwardly disengaging the two contacts and thus opening the load circuit. The resultant cooling of the strip portion will cause the vane to snap back and re-engage the contacts but the latter will be immediately reopened, by snap action of the vane, should the fault in the load circuit not be cleared. As soon as the fault in the load circuit is cleared so that there is no longer an excessive current drain in the load circuit, the vane will remain stationary and the contacts will remain closed.

For an understanding of the invention principles, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

FIG. 1 is a plan view of a vane used in the automatic re-set circuit breaker of the invention, this vane being identical with that shown in FIG. 4 of my abovementioned patent;

FIG. 2 is a longitudinal sectional view through an automatic re-set circuit breaker embodying the invention;

FIG. 3 is a sectional view taken on the line 33 of FIG. 2; and

FIG. 4 is a view similar to FIG. 3 illustrating a modification of the invention.

Referring first to FIG. 1 of the drawing, the circular vane .10 therein is cut from a piece of preferably electrically conductive spring metal selected for high elasticity and resistance to creep under static or dynamic stresses. Also, the particular metal is selected with respect to its specific temperature resistance, coefficient of resistance, and coefiicient of expansion, these factors all needing to be taken into account to produce a vane which will carry a pre-set current without deflecting but which will deflect when the current carried thereby exceed-s such preset value or rating of the circuit breaker.

Vane 10 is formed with a closed end slot 11 extending in parallel, relatively close relation to the circumference of the vane and throughout substantially degrees. Slot 11 forms a narrow arcuate strip 15 along the circunrference of the vane and integral at each end with the relatively larger main body section 12. Ridges 20 are tilinear zones, such as formed by the ridges or embossrnents 20, accomplishes several purposes. In the first place, the thinning of the vane material sets up substantial external pressures along the general line of the embossments. In the second instance, the spacing of the inner ends of the embossments creates a focal point or area so that the vane, when operating, will break down at a pre-determined point or area.

The central area between the inner ends of the ridges 2b is kept unmarred as most of the flexing will occur in this area. The bending stresses are also kept away from this central area. Keeping this central area free of stresses result in stable operation of the vane being maintained effectively over a relatively long period of time. The depth of the embossments and the consequent thinning of the vane material is dependent upon the desired operating parameters of the vane.

Furthermore, the deformation of the main body section 12 results in an initial'sct being imparted to the vane along a bending line determined by the direction of the deformations. The strip 15 is then foreshortened by forming an otf-set16 therein at or adjacent its center. This foreshortening of strip 15, which strip is integral at each end with body section .12, results in stressing the main body section to bend about a line normal to the strip and at an angle to the initial bending of the body section.

If vane is heated, as by an electric current flowing therethrough, the strip heats and expands much faster than main body section 12. The differential expansion of strip 15 relative to body section 12 progressively decreases the stress holding the main body section bent about a line normal to the strip, and the main body section 12 flattens to a point where it snaps to a position bent about its initial bending line as determined by the direction of ridges 20. As the vane cools, the differential contraction of the strip relative to the main body section 12 again stresses the latter to bend about the line normal to the strip and, after an equilibrium of forces is reached and just passed, the vane snaps back to its V-shape bent about the line normal to the strip 15.

The snapping of the main body section 12 between positions bent about a pair of different axes or lines results in'a substantial amplitude of relative movement between selected points or areas of the main body section and selected points or areas of the strip. This may be utilized to advantage by mounting the vane 10 at a point fixed relative to strip .15, and mounting a contact at the center of vane 16 this contact being engageable with a contact forming part of an electric circuit for heating the vane.

Referring to FIGS. 2 and 3, the automatic reset circuit breaker utilizing the vane 10 is illustrated as having the general shape and dimensions of the usual plug fuse. Thus, the circuit breaker includes a dielectric material hollow body 21 on which is conformingly embraced by a conductive metal shell 22 having a threaded configuration. The inner or bottom end of body 21 is closed, as at 23, and has a terminal or contact 24 on its outer surface and centrally thereof, as in the case of the usual plug fuse.

A contact 25 is secured to the undersurface of vane 1d at the center thereof and engages a contact 26 which is a fixed contact connected by a conductive post 27 to contact 24. Vane 1b is mounted fixedly relative to body 21, and with contact 25 in engagement with contact 26, by a conductive metal bar or strip 28 in electrical and mechanical connection with shell 22 and secured at its inner end, as by spot welding or brazing, to strip 15, preferably at deformation 16.

As schematically illustrated, the circuit breaker is arranged to control a circuit extending between terminals 3t? and including a conductor 31 connected to shell 22, as by being connected to a receptacle into which shell 22 is threaded, and a conductor 32 connected to contact 24 as by being a contact in the base of such receptacle. As mentioned above, the parameters of vane 10 are so selected that, with normal flow of current between terminals 30, the vane 10 is heated insufficiently to expand strip 15 to a point where the vane will snap, and is so positioned that contacts 25 and 26 are maintained in pressure engagement. Thus, the circuit remains closed between terminals 3tb so long as the current flow in such circuit does not exceed a pre-set value which the circuit breaker is pre-rated to carry without opening. However, should a fault occur in the circuit between terminalsdb, the excess current fiow above the pre-set value will heat vane 14 sufficiently to cause the latter to snap to the dotted line position of FIG. 2 and disengage contacts 25 and 26 to open the circuit. As thevane cools, it snaps back to its solid line position to re-engage the contacts 25 and 26 but will immediately snap to the open position should the fault not be cured in the load circuit.

This intermittent opening and closing of the load circuit will continue for as long as the fault in the circuit con tinues. When the fault is cleared, the vane will snap to the contact closing position and will maintain the contacts closed.

In the form ofcirc-uit breaker shown in FIG. 4, parts identical with those of FIGS. 2 and 3 have been given the same reference characters, and parts corresponding to those of FIGS. 2 and 3 have been given the same reference characters primed. In this embodiment of the invention, the vane 10' is formed the same as the vane it) but, in this case, a high resistance heatingwinding 35 is wound about strip 15 and connected at one end to this strip. The other end of winding 35 is connected to shell 22. Vane 10 is supported from a strip or bar 28" to which strip 15 is secured, and bar 23' isins'erted or em bedded in body 21 but does not make either electrical or mechanical contact with conductive metal shell 22..

The current through the vane flows through the heating winding 35 and this heating winding effects the expansion of strip 15, as distinguished from the case of FIGS. 2 and 3 Where the current directly heats strip 15. Theme of the heating winding Bid-enables a more accurate pre-setting of the current value which the circuit breaker will carry without opening. Other than the foregoing modifications, the circuit breaker of FIG. 4 operates in the same manner as does the circuit breaker of FIGS. 2 and 3.

From the foregoing, it will be seen that a novel and inexpensive automatic re-set circuit breaker has been provided which is essentially as simple and inexpensive in construction as is the usual plug type fuse used to control household and automotive vehicle circuits. It will be further noted that the circuit breaker opens and closes as long as the fault continues and remains closed only when the fault is cleared.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the invention principles, it will be understood that the v invention may be embodied otherwise without departing from such principles.

What is claimed is:

An automatic re-set circuit breaker usable interchangeably with the usual plug type fuse, comprising, in combination, a hollow substantially cylindrical body of dielectric material having a closed end; a first terminal at the center of such closed end and exposed externally thereof; a substantially cylindrical shell of conductive metal embracing the side wall of said body and having a threaded configuration and constituting a second terminal; a first contact fixedly mounted in said body and electrically connected to one of said terminals; an electrically conductive substantially circular monometal snap action vane having a relatively fixed peripheral portion thereof fixedly mounted in said body and a relatively movable body portion carrying a second contact normally pressed against said first contact; and means electrically connecting said vane to the other of said terminals; said relatively movable vane body portion, upon flow of current through said vane in excess of a preselected value, snapping, relative to said peripheral portion, to a position disengaging said contacts; said vane, upon cooling due to interruption of current flow therethrough, snapping said relatively movable body portion to a position ire-engaging said contacts under pressure; said vane including a thermostatic pull strip integral therewith and constituting said peripheral portion, and normally constraining said relatively movable body portion to a position maintaining said contacts engaged under pressure; said pull strip being formed by a reiatii ely narrow arcuate slot in said vane adjacent but spaced a short distance from the vane circumferential periphery.

References ited in the file of this patent UNITED STATES PATENTS 

